1. Field of the Invention
The present invention relates to a high-pressure fuel injection pipe which is in use connected to a common rail system or a P-L-D (pump line delivery) injection system (hereinafter referred to as the P-L-D injection system) for a diesel internal combustion engine.
2. Description of the Prior Arts
This kind of diesel engine fuel injection pipe has heretofore included, for example, a truncated conical connecting head 12 which has a seat surface 13 made of an outside circumferential surface formed at the end of a thick-walled steel pipe 11 as shown in FIG. 13, or a truncated conical connecting head 22 which has a seat surface 23 made of an outside circumferential surface formed at the end of a thick-walled steel pipe 21 as shown in FIG. 14. Each of the truncated conical connecting heads 12 and 22 is formed by buckling under axial pressure which is applied from the outside by a punch member, and at the same time a circumferential wall of each of the connecting heads 12 and 22 is expanded outwardly by buckling under such axial pressure, whereby an annular pocket 15-1 (FIG. 13) or an annular notch 15-2 (FIG. 14) is formed in the inside of the connecting head 12 or 22. The diesel engine fuel injection pipe is at present in use in the above-described state. Incidentally, reference numeral 14 denotes a sleeve washer fitted to the back of the connecting head, and reference numeral 16 denotes a clamping nut.
In a fuel injection system which adopts such a diesel engine fuel injection pipe, the diesel engine fuel injection pipe is made short in order to inject a sufficient amount of fuel into a combustion chamber without causing pressure loss in the pipe as well as in terms of the convenience of piping. However, even in such a short injection pipe, when a valve is closed after the injection of fuel, pressure variations occur in the injection pipe. These pressure variations reach even a common rail through the pipe in the form of pulsations, and further affect the next cylinder. This leads to the problem that the fuel injection pipe cannot effect stable injection of fuel.
As a countermeasure against this problem, it is possible to reduce the pressure variations, as by enlarging the inner diameter of the injection pipe or the common rail to increase the volume of the pipe. However, there occurs the disadvantage that pulsations propagate fast. In order to suppress the pulsations and make the propagation thereof slow and small, the methods of forming orifices in common rails have been developed. Two methods are known as such methods. One of the methods is to make far smaller the diameter of each branch hole formed in a common rail and give orifice functions to the respective branch holes, while the other is to insert a metal ring member (piece) having an orifice into each branch hole portion of a common rail. Either method is capable of suppressing pulsations and making the propagation thereof slow. However, the method of making far smaller the respective diameters of branch holes in a common rail and giving orifice functions to the respective branch holes has the disadvantage that since repetitive high pressures are applied to the branch hole portions, a wall thickness of a minimum of 7 mm or more is needed, and also since machining must be performed at a location deep under the peripheral surface of the common rail, orifices are not easy to form. The method of inserting a metal ring member (piece) having an orifice into each branch hole portion has the disadvantage that two portions, i.e., the portion between the common rail and the metal ring member and the portion between the injection pipe and the metal ring member, are sealed by the axial force of one clamping nut incorporated in the injection pipe, but the resultant sealing is poor in stability.
The present invention has been made to solve the above-described problems, and provides a diesel engine fuel injection pipe which has an orifice pipe provided at its end portion so as to suppress pulsations, make the propagation thereof slow and small, and effect stable injection of fuel.
According to the gist of the present invention, an orifice pipe having an outer diameter smaller than or equal to the diameter of a pipe passage of the fuel injection pipe is disposed at an end of the fuel injection pipe or in the interior of the fuel injection pipe near the end thereof, on at least one side, preferably, a common-rail side in the case of a diesel engine fuel injection pipe which has a head having a conical or spherical seat surface and a clamping nut, or in the interior of the fuel injection pipe near a pump-side end thereof in the case of a P-L-D injection system.
The orifice pipe may be secured in the interior of the fuel injection pipe by an external diameter-reducing force. Otherwise, the orifice pipe may have a projecting portion one end of which projects outward from the end of the fuel injection pipe. Otherwise, the orifice pipe may have a flange portion having a diameter larger than the diameter of the pipe passage. Otherwise, the orifice pipe may be made of a hard-metal-made. pipe body and a soft-metal-made ring fitted on one end of the pipe body which projects outward from the end of the fuel injection pipe. Otherwise, the orifice pipe may be made of a hard-metal-made inner pipe and a soft-metal-made outer pipe having a flange portion which projects outward from the end of the fuel injection pipe.
In other words, according to the present invention, the orifice pipe is disposed at or inward of the end opening of the connecting head of the fuel injection pipe, and this orifice pipe serves the role of an orifice and makes it possible to suppress pulsations, make the propagation of pulsations slow and small, and effect stable injection of fuel without affecting sealing performance. In addition, since the flange portion or the ring is made of a soft metal, the axial force of the clamping nut is prevented from being cancelled and a decrease in sealing surface pressure is prevented.
In the present invention, means for fixing the orifice pipe may be press fitting, caulking, rolling, shrinkage fitting, soldering, welding or the clamping of the flange portion between the orifice pipe and a mating seat surface.